I recently completed this ZCI for my table saw. It’s made from half inch plywood and sch 40 2” PVC pipe. Thanks to Izzy Swan for giving me the design to modify for my saw! It’s solid, smooth and works great. The only issue I have with it is that it’s warped slightly, causing it to rock in the table. Is there a way to flatten it without rebuilding the ZCI? This one was much more complicated to make than would be a ZCI for a cabinet saw, so would rather flatten it than redo the whole thing.

It has always been my understanding that when you laminate plywood, you need to laminate both sides to prevent warping. I use formica for the same reasons you like pvc—red on top and gray on the bottom.

-- John C. -- "Firearms are second only to the Constitution in importance; they are the peoples' liberty's teeth." George Washington

“It has always been my understanding that when you laminate plywood, you need to laminate both sides to prevent warping. I use formica for the same reasons you like pvc—red on top and gray on the bottom.”

Oh, I forgot to mention that! The PVC is held on with screws, not laminated.

Laminated or not covering one side of wood with a moisture barrier is going to make things warp. If you were right you wouldn’t be asking for help, now would you? Being a smart arse isn’t going to make folx want to help.

Perhaps you should drill access to the adjustment screws specifically for levelling the ZCI?

I assume there was a time when the insert was flat and sat perfectly flush with the table saw top. If this is the case, then it is likely that the plywood substrate has twisted. However, since the PVC is screwed to the plywood, separating the parts could pinpoint the component that failed. If the PVC is twisted, then obviously it needs to be re-flattened. More likely the plywood is twisted and the PVC has remained flat. A trip to the jointer could flatten the face of the plywood to which the PVC is attached. The twist remaining in the underside of the plywood does not appear to be a problem since it looks like the insert rests on the PVC lip when installed in the table saw.

If idea fixes the problem now, the twisting problem could re-occur later. Moisture is able to enter and exit the plywood substrate from the edges and underside to a much greater extent than on the upper side of the plywood and thus distort the plywood. Therefore I would think that applying a few coats of a film finish like polyurethane to the edges and the underside of plywood substrate could be help stabilize the insert. I am not sure that applying a film finish to the upper side of the plywood substrate is required or even be a good idea, since the PVC blocks moisture exchange on the upper surface (even when the PVC is just screwed in place).

If the PVC is still flat, the making a new backer from a more stable material could be required. One material that comes to mind is MDF.

When I made zero clearance insert, I made a batch. I use some for various widths of dados while a few others remain uncut for later use.

I am a bit puzzled as to why Izzy and you used a plywood substrate. Mixing materials always seems to lead to problems. I would think that laminating two or three pieces of flattened PVC would have been a better approach.

Even simpler than laminating layers of PVC (while I wonder if a flattened piece of PVC pipe retains any memory) why not run down to Wallyworld or where ever and pick up a poly cutting board for a few bucks. It mills easily, low friction, stiff, and flat. What ever you do, don’t do like I did and steal one from the kitchen when you needed some miter slot bars for your sled.

Jbrow: Thank you for mentioning MDF, I have a bunch of it from an old Walmart bookcase we had before I built the log one. I’ll try that ASAP. It also didn’t really accur to me that even though it wasn’t sealed, it would slow down the moisture exchange. I was thinking more of cross grain expansion when I built it. This was warped as soon as it was assembled, so it’s definitely just the plywood.

MuleSkinner: I tested that, and PVC doesn’t seem to retain memory as long as it doesn’t overheat. However, I was amazed to see it reform into its exact shape upon being heated too 350 Degrees. I guess that means if I ever need to repair the plumbing, I can just grab my insert plate and stick it in the oven rather than buying a new pipe :-)